Method of plating copper



Patented July 8, 1952 JnhrrEcBaavcr. Osborn, Ohio Nonrawlng. Application May 11, 1948, Serial No. 26,475

high luster'so that hurling of the surface is not necessary.

It is another object of this invention to provide a bright copper deposit by electrolysis from an acid. bath with which operation can be satisfacinfily-continued over a lonaneriod of time without. noticeable, deterioration oi the bath; or impairmentoi the coating.

It is still another object 01 this invention to provide a bright copper deposit by electrolysis of an acid bath with which. an electric current of high density may be used.

It isstill another object of thislnvention to provide a bright copper deposit by electrolysis of an acid bath does not requirefrequent renewal. of the electrolyte and. discarding of the bath used.

It is still another object. oi. this invention to provide a bright copper deposit. by electrolysis using, an acid bath whichdoes notbecometurbid after some time so that a filtering stendoes not have to be inserted from time to time.

It is still another object of this invention to provide a bright copper deposit by electrolysis using an acid bath which has a highly increased tolerance for impurities.

It has been found by the applicant during comprehensive research work that, while electrolytes based on a mixture of copper sulphate and sulfuric acid operate satisfactorily in the beginning, the deposits become less and less uniform as the operation continues. This phenomenon was even noticed although the proportions of the ingredients oi the bath were constantly kept at the same level. As a consequence of the disadvantage just described the electrolyte had to be discarded at frequent intervals and replaced by a new one.

After a great many experiments it was discovered that the change of the content of chloride anion is responsible for such unsatisfactory operation.

After this discovery it was then found out that 2 the electrolytes when first usediingthe hes had a very low content of chloride anions which were present in the form of. acontamination but that this chloride content became gradually depleted. This was when the opora km s artedt become unsatisfactory.

Further studies of the problem revealed that it the chloride anion content of the electrolyte is controlled, so as to bring it within a range of from 0.001 to 0.015 gram per liter of electrolyte all these disadvantages are. overcome. A bath thus composed yields deposits of the desired properties for a very considerable, period oftime.

The essence of the inventlonthus consistsyin providing an electrolyte for acid copper plating in which the.chloric le. anion content ranges from 0.001 to 0.0115 gram per liter.

As. has been mentioned above the predominant ingredients of: the bath preferred for the electrolysis are copper sulphate andsuliuri'c acid.

It is advantageous to add a brightening agent to the elecrtolyte; derivatives of; thiourca. ha been found especial y suitable. to: this purpose. and in particular acetyl thlourea has yielded excellent results.

It is also advantageous, though cutionahtaadd an agent which permits the use of an electric current of high density. .nentrim molasses. and caramel are excellenttor Sometimes it is also to add ,a .1 flung a ent; so i l ryl sulfateandsodium ocit'lsidfate are preferred therefor.

The invention thus consists in an electrolytic bath which contains 1 to 275 grJl. copper sulfate 20 to grJl. sulfuric acid 0.001 to 0.015 gr./l. chloride anion 0 to 1.0 gr./l. caramel. dextrin and/or molasses 0.005 to 0.05 gr./l. of acetyl thiourea The articles to be plated are advantageously subjected to a preliminary treatment prior to the coating proper. For this purpose they are cleaned with an alkaline cleaner, dipped into acid in order to remove any rust, nuetralized and then rinsed in water. It is also preferable to first apply a thin copper coating from a cyanide both. such a bath may contain from 3 to 5 ounces of copper metal per gallon, 1% to 3 ounces of free sodium cyanide and from 2 to 8 ounces of sodium carbonate. Plating with this bath for from 3 to 4 minutes is suilicient. After this flash plating the article is washed to remove the cyanide.

It is furthermore advantageous to agitate the electrolyte during electrolysis. This may be carried out either by moving the cathode or by stirring the electrolyte, the latter being preferred. In particular has it been found satisfactory to effect stirring by blowing air through the bath. If stirring is carried out this way, however, it is advisable to restrict the quantity of the wetting agent to a minimum or omit it entirely, because otherwise excessive foaming takes place which impairs the operation.

The temperature of the bath is preferably maintained at between 80 and 100 F. The electric current should have a voltage of from 2.5 to 6 volts and a density of from 40 to 200 amps. per square foot.

In the following, two examples are given for the purpose of illustrating my invention:

Example I An electrolyte was used having the following composition:

35 i gin/i. CuSOefiHaO Bligh/l. sulfuric acid 0.005gr./l. chloride anion 0.10 gr./1. dextrin 0.015 gr./l. acetyl thiourea 0.02 gr./l. sodium octyl sulfate The bath had a temperature of 95 F. Agitation was carried out by blowing air through the bath. vThe electric current had a density of 100 amps.

per sq. ft. and a voltage of 4.5 volts.

The coating obtained in this instance was extremely smooth and uniform and had a high luster. The bath did not show any turbidity even after a use of several weeks.

The tolerance for impurities for a bath of this invention is considerably increasedinparticular for iron, zinc, chromium and nickel. For instance, without the presence of chloride anions, an iron content of 0.25 gr/l. is harmful and impairs the operation. With a chloride anion content is set forth in this specification several grams per liter may be present in the electrolyte and the operation will still be satisfactory.

Example II 200 gr./l. copper sulfate 50 g g/l. sulfuric acid 0.005 gr./l. chloride anion The process with this electrolyte was carried out under the same conditions as were used in connection with Example I with the exception 4 that agitation of the electrolyte was effected by moving the cathode instead of introducing air. The same favorable results were obtained.

It will be understood that while there have been described herein certain specific embodiments of my invention, it is not intended thereby to have it limited to the details given in view of the fact that this invention is susceptible to various modifications and changes which come within the spirit oi the disclosure and the scope of the appended claims.

I claim:

1. In a method of electrolytically depositing copper from a copper sulfate-sulphuric acid bath containing acetyl thiourea in an amount of from about 0.005 to 0.05 gm./l. and chloride anion in an amount of from about 0.001 to 0.015 gm.'/l., the step of maintaining the chloride anion concentration at a constant value within the range of about 0.001 to 0.015 gm./l. by addition of a chloride.

2. In a method of electrolytically depositing copper from a copper sulfate-sulphuric acid bath containing a thiourea compound in an amount of from about 0.005 to 0.05 gm./l. and chloride anion in an amount of from about 0.001 to 0.015 gm./1., the step of maintaining the chloride anion concentration at a constant value within the range of about 0.001 to 0.015 gm./l. by addition of a chloride.

JOHN F. BEAVER.

REFERENCES drum The following references are of record in the pp. 457-458. I

Buswell: Chemistry of Water and Sewage Treatment, 1928,,pp..74-76.

Operating Manual Daybrite Acid Copper 'Proc ess, pp. 2-3. 

1. IN A METHOD OF ELECTROLYTICALLY DEPOSITING COPPER FROM A COPPER SULFATE-SULPHURIC ACID BATH CONTAINING ACETYL THIOUREA IN AN AMOUNT OF FROM ABOUT 0.005 TO 0.05 GM./L. AND CHLORIDE ANION IN AN AMOUNT OF FROM ABOUT 0.001 TO 0.015 GM./1., THE STEP OF MAINTAINING THE CHLORIDE ANION CONCENTRATION AT A CONSTANT VALUE WITHIN THE RANGE OF ABOUT 0.001 TO 0.015 GM./L. BY ADDITION OF A CHLORIDE. 